Welcome

The title says it all: this blog features physics videos found everywhere on the web: animations, demonstrations, lectures, documentaries.

Please go here if you want to suggest other nice physics videos, and here if I mistakingly infringed your copyrights. If you understand French, you'll find a huge selection of physics videos in French in my other blog Vidéos de Physique.

Wednesday, 29 January 2014

Demonstration of an optical technique that allows us to see small changes in the index of refraction in air. A point source of light is reflected from a concave mirror and focused onto the edge of a razor blade, which is mounted in front of the camera. Light refracted near the mirror and intercepted by the blade gives the illusion of a shadow.

Seen here are the heated gases from a candle flame and a hair dryer, helium gas, and sulfur hexafluoride gas.

The earth contains a great many natural radioactive elements (such as uranium, thorium and potassium). Uranium, for example, is present in all rocks, and in particular granite rocks. When it decomposes, it gives rise to a radioactive family, ultimately forming lead, which is stable. Radon is one of the radioactive decay products of uranium. Its distinguishing sign is that it is a gas.

And as it is a gas, it escapes and accumulates in caves or galleries, which are enclosed spaces. During the first few years when French uranium deposits were mined, the miners breathed air in which the radon content could be as high as 20,000 Becquerels per cubic meter. Epidemiological studies on uranium miners have shown that radon is a carcinogenic agent that can cause lung cancer. More recently, studies on the general population have confirmed this risk for exposure to radon in the home.

"How fast are you moving?" seems like an easy question, but it's actually quite complicated -- and perhaps best answered by another question: "Relative to what?" Even when you think you're standing still, the Earth is moving relative to the Sun, which is moving relative to the Milky Way, which is...you get the idea. Tucker Hiatt unravels the concepts of absolute and relative speed.

Tuesday, 21 January 2014

If you were to orbit the Earth, you'd experience the feeling of free fall, not unlike what your stomach feels before a big dive on a roller coaster. With a little help from Sir Isaac Newton, Matt J. Carlson explains the basic forces acting on an astronaut and why you probably shouldn't try this one at home.

Sunday, 19 January 2014

This video of the sun based on data from NASA's Solar Dynamics Observatory, or SDO, shows the wide range of wavelengths -- invisible to the naked eye -- that the telescope can view. SDO converts the wavelengths into an image humans can see, and the light is colorized into a rainbow of colors.

As the colors sweep around the sun in the movie, viewers should note how different the same area of the sun appears. This happens because each wavelength of light represents solar material at specific temperatures. Different wavelengths convey information about different components of the sun's surface and atmosphere, so scientists use them to paint a full picture of our constantly changing and varying star.

Yellow light of 5800 Angstroms, for example, generally emanates from material of about 10,000 degrees F (5700 degrees C), which represents the surface of the sun. Extreme ultraviolet light of 94 Angstroms, which is typically colorized in green in SDO images, comes from atoms that are about 11 million degrees F (6,300,000 degrees C) and is a good wavelength for looking at solar flares, which can reach such high temperatures. By examining pictures of the sun in a variety of wavelengths -- as is done not only by SDO, but also by NASA's Interface Region Imaging Spectrograph, NASA's Solar Terrestrial Relations Observatory and the European Space Agency/NASA Solar and Heliospheric Observatory -- scientists can track how particles and heat move through the sun's atmosphere.

The 2.9 minute movie was created by NASA's Scientific Visualization Studio or SVS at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and is available at the SVS website: http://svs.gsfc.nasa.gov/goto?11385

Thursday, 16 January 2014

In the late 1940s, Bell Laboratories scientists John Bardeen, Walter Brattain, and William Shockley invented the transistor, the first solid-state amplifier or switch, and in doing so laid the foundation for all modern electronics and circuitry. The three shared the Nobel Prize in Physics in 1956 for the achievement. It may be the most important invention of the 20th century.

This 1965 film shows footage of them reunited/recreating their 1940s lab time to show how it was done, but in real life they had parted. Bardeen had left the labs in 1951 for the U. of IL; Shockley in 1956 to run a semiconductor company in California (laying the groundwork for Silicon Valley), and Brattain retired in 1967 to Whitman College.

Wednesday, 15 January 2014

On December 28, 1895, the German physicist Wilhelm Conrad Röntgen announced he had discovered rays which he called X. With these rays, we can see inside objects, and when the hand is interposed, it is the bones that appear!

For the public, these rays are a source of entertainment. For doctors, they offer a revolutionary technique for exploring the human body. Many of these pioneers who use X-rays are victims of radiation dermatitis, or burns to the hands that, in the most severe cases, lead to amputations and even death.

Regulation of the use of X-rays and implementation of radiation protection measures would not come before the late 1920s.

Tuesday, 14 January 2014

Picking up the work of the French physicist Henri Becquerel, Pierre and Marie Curie give the name "radioactivity" to the property possessed by certain elements of spontaneously emitting radiation. In 1898, Marie isolates polonium and radium, both of then unknown and highly radioactive elements.

Medicine grabs radium and makes it the tool in the fight against cancer. Praised for its benefits, radium becomes a source of rejuvenation for the public and a source of profit for manufacturers. It will take time and evidence to admit the danger of its radiation...

Sunday, 12 January 2014

The shape, contents and future of the universe are all intricately related. We know that it's mostly flat; we know that it's made up of baryonic matter (like stars and planets), but mostly dark matter and dark energy; and we know that it's expanding constantly, so that all stars will eventually burn out into a cold nothingness. Renée Hlozek expands on the beauty of this dark ending.

Carl Sagan's oft-quoted statement that there are "billions and billions" of stars in the cosmos gives an idea of just how much "stuff" is in the universe. However scientists now think that in addition to the type of matter with which we are familiar, there is another kind of matter out there. This new kind of matter is called "dark matter" and there seems to be five times as much as ordinary matter. Dark matter interacts only with gravity, thus light simply zips right by it. Scientists are searching through their data, trying to prove that the dark matter idea is real. Fermilab's Dr. Don Lincoln tells us why we think this seemingly-crazy idea might not be so crazy after all.

According to Pete is a video segment starring SparkFun Director of Engineering Pete Dokter. In this video series, Pete addresses common engineering questions, discusses current projects, and explores the wide world of embedded electronics!

Astronauts on the ISS are experimenting with a form of water that has a strange property: it can help start fire. This fundamental physics investigation could have down-to-Earth benefits such as clean-burning municipal waste disposal and improved saltwater purification.